This invention relates to ring laser angular rate sensors, and more particularly to a ring laser readout mechanism.
Ring laser angular rate sensors are well known in the art of inertial navigational systems. Some examples of ring laser angular rate sensors are shown and described in U.S. Pat. Nos. 3,373,650; 3,390,606, 3,467,472 and 4,152,071, all of which are assigned to the assignee of the present application. Sensors as those described in the aforementioned patents utilize what is sometimes referred to as a double beam signal for providing sensor information. The double beam signal is essentially a portion of each of the counterpropagating laser beams emerging from the laser angular rate sensor. The emerging double beam signal provides an interference pattern useful for rate information. If the portion of each beam of the double beam signal which emerges is colinear, a spot interference pattern is created. On the other hand, if the portion of each beam which emerges is at a slight angle, an interference pattern of lines is created. When the interference pattern is projected on a detector, such as a photodetector, angular information may be obtained by counting the interference pattern maxima and rate information may be obtained by measuring the time difference between maxima.
As disclosed in U.S. Pat. No. 4,152,071, rate information is also available in a single beam signal since the intensity of a single beam is modulated at the beat frequency between the waves or beams which is directly related to the angle of rotation of the sensor. The latter type of beat information, although useful for obtaining sensor rate information, is particularly useful in providing a signal indicative of the lock-in rate of the sensor and thus is useful in negative feedback control systems for operating the laser angular rate sensor at a minimum lock-in rate.
It is an object of the present invention to provide a readout mechanism for a ring laser angular rate sensor having both double beam output signals and single beam signals.